1. Field of the Invention
The present invention relates to an electronic endoscope apparatus. More particularly, it relates to a configuration for supplying power and video signals between an electronic endoscope which is a scope and a processor unit which is connected with the electronic endoscope as well as for sampling the image signal properly.
2. Description of the Related Art
In an electronic endoscope apparatus, an electronic endoscope equipped, for example, with a CCD (Charge Coupled Device) which is a solid-state image sensor is connected to a processor unit via a cable and connector. Through these cable and connector, power is supplied and various control signals are transmitted from the processor unit to the scope while a video signal and various control signals are transmitted from the scope to the processor unit.
Thus, the scope is driven by DC power supplied from the processor unit via a power line while a video signal picked up by the CCD of the scope is transmitted to the processor unit via a signal line (transmission line). As the processor unit performs various types of color video processing on the video signal, images of the object under observation are displayed on a monitor.
However, with the electronic endoscope apparatus described above, the cable connecting the scope with the processor unit contains a power line and a plurality of signal lines. Consequently, the connector of the cable has a multi-pin architecture, which may cause bad connections or breakage of some connection pins in addition to being expensive.
Recently, CCDs equipped with scopes have been growing in pixel count. This requires an ability to connect various scopes equipped with CCDs which have increased but different pixel counts to a common processor unit. To deal with this situation, each scope and the processor unit are equipped with oscillators which differ in frequency according to pixel counts, clock signals are approximated by dividing oscillation frequencies or the like, and processing timings in video processing are synchronized between the scope and processor unit. However, when sampling pixel signals outputted from a CCD, in particular, a slight difference in processing timing between the scope and processor unit will make it impossible to obtain a proper video signal.
FIGS. 13, 14A and 14B show configuration and operation of a sampling circuit. A CCD 1 mounted on the scope is connected, for example, with a correlated double sampling circuit 2. The sampling circuit 2 has a sampler 3 and holder 4 and its operation is controlled based on timing pulses (sampling pulses) which are output from a synchronizing signal generator (SSG) 5 and synchronized with operating timing of the CCD 1. For example, output of the CCD 1 is a signal which falls on a pixel-by-pixel basis as indicated by a horizontal line signal in FIG. 14A, and when the signal passes through the sampling circuit 2, its pixel-by-pixel amplitude is held as shown in FIG. 14B and an amplitude envelope of the CCD output shown in FIG. 14A is extracted as a video signal.
However, if there is a phase difference between the timing pulses outputted from the synchronizing signal generator 5 and the timing pulses outputted (read) from the CCD 1, it becomes impossible to accurately pickup the amplitude of sampled pixel signals, resulting in an inability to obtain a proper video signal. Such a phase difference can occur due to temperature conditions, the length of the electronic endoscope (the length of transmission channel), etc. even when oscillators with the same frequencies are used.
Furthermore, electronic endoscope apparatus are sometimes provided with an electronic shutter function which controls brightness of video by adjusting charge accumulation time of the CCD 1. It is necessary for an electronic endoscope apparatus to implement the electronic shutter function to work.
The present invention has been made in view of the above problems. Its object is to provide an electronic endoscope apparatus which can use a common line for power supply and signal transmission, connect a scope and processor unit using a minimal number of lines, and form images in good condition by means of accurate sampling even when scopes equipped with CCDs with different pixel counts are connected to a common processor unit as well as can easily implement an electronic shutter function.